Neil Brown (neilb@xxxxxxx) wrote on 21 January 2008 12:15:
>On Sunday January 20, carlos@xxxxxxxxxxxxxx wrote:
>> A raid6 array with a spare and bitmap is idle: not mounted and with no
>> IO to it or any of its disks (obviously), as shown by iostat. However
>> it's consuming cpu: since reboot it used about 11min in 24h, which is quite
>> a lot even for a busy array (the cpus are fast). The array was cleanly
>> shutdown so there's been no reconstruction/check or anything else.
>>
>> How can this be? Kernel is 2.6.22.16 with the two patches for the
>> deadlock ("[PATCH 004 of 4] md: Fix an occasional deadlock in raid5 -
>> FIX") and the previous one.
>
>Maybe the bitmap code is waking up regularly to do nothing.
>
>Would you be happy to experiment? Remove the bitmap with
> mdadm --grow /dev/mdX --bitmap=none
>
>and see how that affects cpu usage?
OK, I just removed the bitmap (checked with mdadm -E on one of the
devices) and recorded the cpu time of the kernel thread. Tomorrow I'll
look at it again.
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